I've never done any static car photography so i'm just going on the type of shots i like the look of best.
I dunno if you've been doing this already but you could try thinking about locations more, this would obviously mean you would have to have access to the car you were photographing so you could take it to where you wanted, but then its not like you dont own any interesting cars yourself. Personally i find pictures which make good use of the location to be alot more interesting than the "formulaic" shots your talking about.
I think this shot of martijns does this quite well, I dont even like the TT but this picture just seems right because i think the location suits the car well.
This is another one i think uses the location well.
obviously it takes alot more than finding a good location to get pictures like these, Lighting, post processing and some creativity but they can just be the next thing to move onto once you find your getting bored of finding locations, or you could always go and buy a couple of flashes and get used to lighting shots(although if this was me it would end up being something id just spend loads of money on) then combine that with locations, but by starting to do something different with your photos should keep you motivated as youll always be trying to get better and more creative.
I thought this was a very good tutorial about car photography and even though ive never done any of it myself i find myself thinking about all these different things when looking at pictures on the net.
http://www.mattwatkinson.com/tutorial/